Preliminary results of the characterization of the hydrogen emissions from a water electrolysis plant at pilot scale

Hydrogen has been identified as an essential energy carrier for a future low-carbon economy. However, recent studies have highlighted the indirect impact of hydrogen emissions on climate change, emphasizing the necessity of quantifying hydrogen emissions. It is within this framework that the NHyRA project is being carried out. The European consortium of 14 entities of NHyRA aims to assess potential current and future hydrogen emissions throughout its entire chain value (from production to end uses), develop methods to detect and measure these emissions and provide an inventory where to collect these measurements in addition to validated data that already exist in the literature. 

This work will focus on the potential hydrogen emission sources from a water electrolysis system. Among existing hydrogen production methods, water electrolysis is a promising technology for converting and storing electricity, making it interesting for harnessing intermittent and fluctuating renewable energy sources. Furthermore, several European countries are implementing challenging development plans regarding the capacity of installed electrolysers. Understanding the various factors that can influence the amount of hydrogen released by this technology before it is deployed on a large scale is crucial to minimizing its environmental impact and then adopting effective mitigation strategies on the technology, e.g., new components or control strategies. 

Herein, we first introduce the fundamentals of water electrolysis, and we present the typical overall design of an electrolysis system, which includes the electrolysis stack and all the auxiliaries needed for its proper work, i.e. the so-called “balance of plant”. We then proceed to qualitatively present and categorize the main potential emission sources. We start with the “Vented emissions”, which are emissions needed for the system's proper operation. The analysis includes the description of the main mechanisms that may lead to these types of hydrogen released to the vent, like physical phenomena (e.g. Hydrogen crossover) or emissions coming from a process step (e.g. Hydrogen vented after a purification unit until the quality required for fuel cell application is reached or related to Start-up/shut down procedures). Last, we present the “fugitive emissions”, which include all uncontrolled emissions that come from connections that are not perfectly sealed or permeation phenomena related.  

As a conclusion of the work, we present a methodology to estimate the amount of hydrogen released considering also different operational conditions. Finally, to put all these different types of emissions in perspective, we perform a preliminary assessment of the emissions that would happen for a specific PEM electrolysis system for different power supply configurations.